The present application relates to semiconductor devices, and more particularly to devices which are capable of switching relatively high voltages, e.g. of 50V or more, while remaining reasonably compatible with integrated circuit fabrication techniques.
A MOS-gated transistor referred to as an “oxide-bypassed” VDMOS transistor has been proposed for minimizing the specific on-resistance of devices. See Liang et al., “Oxide-Bypassed VDMOS (OBVDMOS): An Alternative to Superjunction High Voltage MOS Power Devices, 22 IEEE Electron Device Letters No. 8, August 2001, which is hereby incorporated by reference.
The structure shown in FIG. 1 was originally proposed, but several variations of this structure have been suggested. See e.g. Liang et al., “Tunable Oxide-Bypassed VDMOS (OBVDMOS): Breaking the Silicon Limit for the Second Generation”, ISPSD 2002; and Yang et al., “Tunable Oxide-Bypassed Trench Gate MOSFET: Breaking the Ideal Superjunction MOSFET Performance Line at Equal Column Width”, 24 IEEE Electron Device Letters No. 11, November 2003; both of which are hereby incorporated by reference. In the OBVDMOS device shown in FIG. 1, the thick oxide 102 is capable of sustaining the high source-to-drain voltage (between source 120 and drain 130), while the buried pillars 110 of N+ or P+ polysilicon that are located on both sides of the voltage-withstand region 140 help to deplete the voltage-withstand region 140 of n-type carriers when there is a drain-to-source voltage present. For a specific voltage-withstand region width and doping concentration, the thickness of the oxide layer 102 between the N+ or P+ polysilicon 110 and the voltage-withstand region 140 can be selected to deplete the entire voltage-withstand region 140 at peak reverse bias.
Oxide-Bypassed Lateral High Voltage Structures and Methods
The present application describes a variety of lateral high-voltage active device structures and methods, in which field-shaping trench electrodes are capacitively coupled to the voltage-withstand region of a lateral semiconductor device. This provides many of the advantages of an “oxide-bypassed” device in a lateral device structure.
In one class of embodiments the voltage withstand region is itself tapered (wider near the drain end, in a unipolar device), to improve on-state conductivity.
The disclosed innovations, in various embodiments, provide one or more of at least the following advantages:
Improved on-resistance;
High degree of process compatibility with existing low-voltage processes;
Easy fabrication of integrated power devices.